JP2004107865A - Additive for improving paper quality - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an internal additive capable of improving paper quality, such as stiffness and bulkiness, of a pulp sheet. <P>SOLUTION: This internal additive for improving the paper quality comprises a polymer emulsion containing a naturally-occurring cationic polymer (A) and polymer particles (B) comprising a constitutional unit derived from a vinyl monomer. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an internal additive that is useful for improving the paper quality of a pulp sheet.

In recent years, the thickness of paper has been reduced due to the reduction of paper weight, the increase in papermaking speed, and the increased blending of deinked pulp for the purpose of reducing the burden on the environment and reducing transportation costs. While bulky paper is desired, a reduction in paper thickness causes a reduction in stiffness because the stiffness of the paper is proportional to the cube of its thickness.

The stiffness of paper greatly affects the sense of quality, the operability during papermaking and printing, the durability of boxes, etc., and the decrease in stiffness gives a low-grade feeling, such as paper jams and swelling of boxes during operation. cause.

Techniques for improving the stiffness include (1) increasing the unit pulp amount (basis weight), (2) using a paper strength agent, and the like. However, in (1), the required pulp amount increases. (2) has a problem that paper strength (hardness of paper breakage) is improved and stiffness is improved to some extent but does not reach a satisfactory level.

Patent Document 1 discloses an internal additive for paper comprising polymer fine particles of a vinyl monomer or a diene monomer using cationic polyvinyl alcohol having a mercapto group as a dispersant as an internal additive for paper, Patent Document 2 discloses a papermaking additive mainly composed of a grafted starch obtained by graft copolymerizing a monomer containing (meth) acrylamide while maintaining the form of starch particles without gelatinizing the starch. However, they have some improvement in stiffness but are still insufficient.

As a technique for improving the bulk of paper, Patent Literature 3 discloses an ester compound of a polyhydric alcohol and a fatty acid, and Patent Literature 4 discloses a technique in which the degree of water separation is 4% or more and two or more of bulk, whiteness, and opacity. A paper quality improver for improving the stiffness is disclosed, but improvement in rigidity is also desired.
JP-A-8-170296 JP-A-11-302992 Japanese Patent No. 2971447 Japanese Patent No. 3283248

課題 An object of the present invention is to provide an internally added paper quality improver that improves the stiffness, bulk, and the like of a pulp sheet. In particular, an object of the present invention is to provide an internally added paper quality improver useful as a stiffness improver.

The present invention relates to an internally added paper quality improver comprising a polymer emulsion containing a natural cationic polymer (A) and polymer particles (B) containing at least a structural unit derived from a vinyl monomer.

本 The present invention also relates to a pulp sheet in which the above-mentioned internal paper quality improver of the present invention is present on the surface and / or inside of the pulp sheet.

The present invention also relates to a method for improving the paper quality of a pulp sheet in which the pulp is brought into contact with the internal paper quality improving agent of the present invention.

By adding an internally added paper quality improver consisting of an emulsion containing a natural cationic polymer having a cationic group (A) and polymer particles (B) containing at least a constitutional unit derived from a vinyl monomer, the stiffness is improved. Alternatively, it is possible to obtain a pulp sheet having a high bulk or both, and particularly a pulp sheet having a high rigidity.

内 The internally added paper quality improver of the present invention comprises an emulsion containing a natural cationic polymer (A) and polymer fine particles (B) containing at least a constitutional unit derived from a vinyl monomer. Although the reason why the internally added paper quality improver of the present invention significantly improves rigidity and bulk is not always clear, natural polymers have a very similar affinity to pulp because they have a similar structure to pulp. Compared with the agent consisting of synthetic polymer represented by polyvinyl alcohol, which is a technology, and fine particles obtained by polymerizing vinyl monomer, the amount of fixation is remarkably improved, and the wetting and spreading property of the agent on the pulp surface after fixing or during drying and heating is improved. It is presumed that the rigidity and bulk were improved due to an improvement in efficiency and an improvement in immobilizing force at the agent / pulp interface. Since the internally added paper quality improver of the present invention has a remarkable effect of improving rigidity, it is preferably used for the purpose of improving rigidity.

<Natural cationic polymer (A)>
The natural cationic polymer (A) used in the present invention is a polymer obtained by an operation such as extraction or purification from a natural product and a polymer obtained by chemically modifying the polymer. Those having a glucose residue in the polymer skeleton (starch residue, cellulose residue, etc.) are preferred. For example, cationic starch or cationic cellulose (especially those which are water-soluble and whose cation group is a quaternary ammonium cation group) is preferred. And the like. One or more of these may be used alone, or a mixture of two or more may be used.

The cationic group includes an ammonium group or an amino group neutralized with an acid. Preferably, those in which the amino group is neutralized with hydrochloric acid, sulfuric acid, nitric acid, acetic acid, formic acid, maleic acid, fumaric acid, citric acid, tartaric acid, adipic acid, lactic acid and the like are included.

As the cationic starch or the cationic cellulose, for example, those represented by the following formula (1) are preferable.

(Where
A: starch residue or cellulose residue,
R: an alkylene group or a hydroxyalkylene group,
R ¹ , R ² , R ³ : the same or different, and an alkyl group, an aryl group, an aralkyl group or a heterocyclic ring containing a nitrogen atom in the formula may be formed.
X ^-: it represents a counter ion of the ammonium salt.
i: Indicates a positive integer. )

As the starch residue or the cellulose residue, those obtained by removing i hydroxyl groups from starch or cellulose are preferable.

R is preferably an alkylene group or a hydroxyalkylene group having 1 to 12 carbon atoms, more preferably 1 to 3 carbon atoms, and particularly preferably a hydroxypropylene group.

R ¹ , R ² and R ³ are preferably an alkyl group having 1 to 12 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, such as a methyl group, an ethyl group, an i-propyl group, and an n-propyl group. Can be X ^- include Examples of the chlorine, iodine, halogen ions, sulfuric, sulfonic such as bromine, methyl sulfate, phosphoric acid, and organic anions such as a nitric acid. i is determined according to the aforementioned degree of cation substitution.

に お い て In the present invention, the natural cationic polymer is produced by a known method. For example, corn starch or the like is cationized with a water / alcohol system using a cationizing agent, and then neutralized with acetic acid, washed with water, and dried. The molecular weight (aqueous solution viscosity) is generally easily adjusted by adding a strong acid such as hydrochloric acid to the cationized slurry and heating the slurry.

Cationic starch can be obtained, for example, by reacting glycidyltrimethylammonium chloride or 3-chloro-2-hydroxypropyltrimethylammonium chloride with raw starch or modified starch from corn, potato, tapioca, wheat, rice, etc. under alkaline conditions. Can be. It can also be obtained by quaternizing dimethylaminoethylated starch. Further, it can be obtained by reacting starch with 4-chlorobutenetrimethylammonium chloride. On the other hand, cationic cellulose can be obtained, for example, by performing the above reaction on hydroxyethyl cellulose.

(4) The nitrogen content of the natural cationic polymer is preferably from 0.05 to 1% by weight, particularly preferably from 0.07 to 0.9% by weight, from the viewpoint of improving rigidity. From the viewpoint of the rigidity improving effect, the nitrogen weight% (hereinafter referred to as N%) is preferably 0.05% by weight or more, and from the viewpoint of the rigidity improving effect, it is preferably 1% by weight or less. N% is analyzed by the Kjeldahl method (JIS K8001).

The natural cationic polymer should have a low molecular weight within a range that does not impair the effects of the present invention, since high solid differentiation of the emulsion is desired in consideration of productivity, in addition to handling convenience and handling properties. Can be. When the molecular weight of the natural cationic polymer is expressed in terms of the viscosity of an aqueous solution, the viscosity of the aqueous solution at 50 ° C. and 7% by weight (B-type viscometer, rotor No. 2, 60 rpm) is preferably 40 to 10,000 mPa · s. 8,000 mPa · s is more preferable.

The natural cationic polymer may be introduced with a functional group such as an ether group such as a hydroxyalkyl group or an ester group such as an acetyl group for the purpose of preventing aging, as long as the effects of the present invention are not impaired.

In the present invention, for the purpose of improving the polymerization stability and mechanical stability, other than the natural cationic polymer to the natural cationic polymer, for example, a combination of a synthetic cationic polymer and a nonionic polymer may be used. good. The synthetic cationic polymer is preferably cationic polyvinyl alcohol, and the nonionic polymer is preferably a semi-synthetic water-soluble polymer such as methylcellulose, hydroxyethylcellulose, or soluble starch; and a synthetic water-soluble polymer such as polyvinyl alcohol. The amount of the polymer other than the natural cationic polymer is preferably 0 to 100 parts by weight based on 100 parts by weight of the vinyl monomer constituting the polymer particles (B). It is more preferable to use 0 to 50 parts by weight.

<Polymer particles (B)>
The polymer particles (B) used in the present invention preferably have a glass transition temperature (Tg) of at most 90 ° C, more preferably at most 80 ° C. When the Tg of the polymer is 90 ° C. or less, part or all of the internally added paper quality improver contained in the paper is melted in the paper manufacturing process, which is preferable from the viewpoint of the rigidity improving performance. The lower limit of Tg is not particularly limited, but is preferably −10 ° C. or higher.

The Tg of the copolymer can be calculated based on “2.4 Glass transition of copolymer” in “Mechanical properties of polymer” (1969). As the Tg, a numerical value described in “POLYMER HANDBOOK Fourth Edition 1999 by John Wiley & Sons, Inc.” was used.
1 / Tg = ΣWn / Tgn
(Tg: glass transition temperature of copolymer Tgn: glass transition temperature of homopolymer Wn: weight fraction)

ポ リ マ ー The polymer particles used in the present invention contain structural units derived from a vinyl monomer. The content of the constituting vinyl monomer in the polymer particles is not particularly limited, but is preferably from 50 to 100 mol%, particularly preferably from 80 to 100 mol%. Examples of the vinyl monomer include a vinyl compound, a vinylene compound, a vinylidene compound, and a cyclic olefin, and preferred examples include those described below.

(1) Methyl (meth) acrylate ((meth) acryl means acryl, methacryl or a mixture thereof; the same applies hereinafter), ethyl (meth) acrylate, isopropyl (meth) acrylate, (meth) acrylic acid Butyl, isobutyl (meth) acrylate, t-butyl (meth) acrylate and the like, preferably alkyl (meth) acrylates having an alkyl group having 1 to 12 carbon atoms, more preferably 1 to 4 carbon atoms;
(2) Fatty acid vinyl esters comprising an ester of a linear or branched fatty acid having 1 to 18 carbon atoms, preferably 1 to 6 carbon atoms, such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl pivalate, and vinyl alcohol Kind;
(3) (meth) acrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, 2- (meth) acrylamide-2- Anionic monomers having a polymerizable unsaturated group, such as methylpropanesulfonic acid, vinylsulfonic acid, and styrenesulfonic acid, and salts thereof are included. Polycarboxylic acids such as maleic acid, fumaric acid, itaconic acid include acid anhydrides, partial esters, and partial amides or mixtures thereof. Examples of the “salt” include an alkali metal salt (sodium salt, potassium salt, lithium salt, etc.), an alkaline earth metal salt (calcium salt, magnesium salt, barium salt, etc.), an ammonium salt (quaternary ammonium salt, Quaternary alkyl ammonium salts, etc.). Among them, sodium salt is the cheapest and preferable.

(4) (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) Polymerizable unsaturated such as acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, N-vinylpyrrolidone, and N-vinylacetamide And a nonionic hydrophilic group-containing monomer having a group.

(5) An amino group having a polymerizable unsaturated group such as N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide Specific examples thereof include a contained monomer, an acid neutralized product thereof, and a quaternized product thereof. Preferred acids for obtaining the acid neutralized product include hydrochloric acid, sulfuric acid, nitric acid, acetic acid, formic acid, maleic acid, fumaric acid, citric acid, tartaric acid, adipic acid, lactic acid, and the like. Examples include alkyl halides such as methyl chloride, ethyl chloride, methyl bromide, and methyl iodide, and general alkylating agents such as dimethyl sulfate, diethyl sulfate, and di-n-propyl sulfate.

(6) Styrene, α-methylstyrene Among the above vinyl monomers, the use of lower fatty acid vinyl esters is most preferable for improving the rigidity of paper. The method for producing the polymer particles used in the present invention can be obtained by emulsion polymerization, suspension polymerization or dispersion polymerization.

(Polymer emulsion)
In the present invention, in the emulsion, the above-mentioned polymer particles (B) are preferably 5 to 60% by weight, more preferably 10 to 60% by weight in terms of a solid content (solid content) from the viewpoint of easy handling. , More preferably 15 to 55% by weight. The average particle size of the polymer particles (B) is preferably from 0.01 to 50 μm, more preferably from 0.1 to 30 μm, particularly preferably from 0.2 to 20 μm, from the viewpoint of the stability of the emulsion and the adsorptivity to pulp. . The solid content is measured by the method described in Examples described later.

In the paper quality improver of the present invention, in order to improve the polymer stability of the polymer particles (B) and the pulp sheet by effectively adsorbing the polymer particles (B) and improving the rigidity of the pulp sheet, the natural type in the emulsion is used. The ratio of the cationic polymer (A) is preferably from 5 to 200 parts by weight, more preferably from 5 to 150 parts by weight, particularly preferably from 7 to 120 parts by weight, per 100 parts by weight of the polymer particles (B). In this ratio, the weight of the polymer particles (B) is the total weight of all monomers constituting the polymer.

Further, in order to effectively adsorb the polymer particles (B) to the pulp and obtain the auxiliary effect of improving the rigidity by the natural cationic polymer (A), the ratio of the natural cationic polymer (A) in the emulsion is required. Is preferably from 5 to 500 parts by weight, more preferably from 7 to 500 parts by weight, particularly preferably from 10 to 500 parts by weight, per 100 parts by weight of the polymer particles (B).

The emulsion of the present invention preferably contains a dispersion medium in an amount of 40 to 90% by weight, more preferably 45 to 85% by weight. The dispersion medium is preferably water, but may contain a lower alcohol having 1 to 4 carbon atoms. Examples of the lower alcohol include methyl, ethyl, and isopropyl alcohols having 1 to 3 carbon atoms.

Furthermore, in addition to preservatives and disinfectants, fillers such as calcium carbonate, talc and white carbon, pigments and the like may be contained as additives.

(Manufacture of internal paper quality improver)
The emulsion (suspension, water dispersion) of the polymer particles (B) obtained by polymerizing the above-mentioned vinyl monomer is used as the internally added paper quality improver of the present invention.

The polymerization method of the polymer particles (B) may be a general anionic, cationic, nonionic or amphoteric surfactant, a natural, semi-synthetic or synthetic anionic, nonionic, An emulsion polymerization method, a suspension polymerization method, or a dispersion polymerization method using a cationic polymer or the like is preferable.

For example, anionic surfactants such as sodium polyoxyethylene dodecyl ether sulfate and sodium dodecyl ether sulfate; cationic and amphoteric surfactants such as trimethyl stearyl ammonium chloride and carboxymethyl dimethyl cetyl ammonium; Sucrose fatty acid esters such as stearate and sucrose dilaurate, sorbitan esters such as sorbitan monostearate, polyoxyalkylene adducts of sorbitan esters such as polyoxyethylene sorbitan monostearate, and polyoxyalkylene adducts of aliphatic alcohols Nonionic surfactants such as starch and derivatives thereof, cellulose ethers such as ethyl cellulose, cellulose esters such as cellulose acetate, cellulose derivatives, etc. Natural and semi-synthetic polymers; polyvinyl alcohol and derivatives thereof, synthetic polymers maleinized polybutadiene.

Among these, those produced by an emulsion polymerization method, a suspension polymerization method, or a dispersion polymerization method in which a vinyl monomer is polymerized in the presence of the above-mentioned natural cationic polymer (A) are preferable. preferable.

The vinyl monomer is preferably used in an amount of 1 to 70 parts by weight, more preferably 1.5 to 60 parts by weight, particularly preferably 8 to 57 parts by weight, based on 100 parts by weight of the reaction solvent. Preferred examples of the reaction solvent include water and lower alcohols.

As the polymerization initiator, peroxides which are uniformly dissolved in a solvent, organic or inorganic peracids or salts thereof, azobis-based compounds alone or in combination with a reducing agent are used as redox-based ones. Specific examples include, for example, t-butyl peroxide, t-amyl peroxide, cumyl peroxide, acetyl peroxide, propionyl peroxide, benzoyl peroxide, benzoyl isobutyryl peroxide, lauroyl peroxide, t-butyl hydroperoxide. Oxide, cyclohexyl hydroperoxide, tetralin hydroperoxide, t-butyl peracetate, t-butyl perbenzoate, bis (2-ethylhexyl peroxydicarbonate), 2,2′-azobisisobutyronitrile, Nylazotriphenylmethane, 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, sodium persulfate, potassium persulfate, ammonium persulfate, hydrogen peroxide, persulfate and triethylamine, triethanolamine, dimethyl Examples thereof include a combination with a tertiary amine such as aniline. The amount of the polymerization initiator used depends on the system used, but it is preferable to use 0.05 to 3 parts by weight based on 100 parts by weight of the vinyl monomer.

The reaction temperature is preferably 30 to 90 ° C, and the reaction time is preferably about 30 minutes to 10 hours.

In the present invention, the emulsion after the completion of the reaction can be used as it is as an internally added paper quality improver.

(4) When a dispersion or emulsion stabilizer other than the natural cationic polymer (A) is used, the natural cationic polymer (A) is added to the emulsion after polymerization, preferably at room temperature, and mixed. Even when the natural cationic polymer (A) is used as a dispersant or an emulsion stabilizer, the natural cationic polymer (A) may be further added to the emulsion after the polymerization.

In the present invention, an additive such as a pH adjuster may be used at the time of polymerization in order to improve polymerization stability, mechanical stability, storage stability and the like. As the pH adjuster, an acid such as phosphoric acid or tartaric acid or an aqueous alkali solution such as sodium hydroxide or potassium hydroxide is added to the polymerization system.

(How to improve paper quality)
In the present invention, the above-mentioned emulsion is mixed with pulp, preferably at room temperature, and the paper is made, whereby the emulsion containing the polymer particles (B) and the natural cationic polymer (A) are separately added to pulp to make paper. Even in this case, a pulp sheet containing the internal paper quality improver of the present invention on the surface and / or inside of the pulp sheet can be obtained.

(4) The amount (addition amount) of the internally added paper quality improver is preferably 0.05 to 20 parts by weight, more preferably 0.1 to 10 parts by weight, based on 100 parts by weight of pulp in terms of solid content. The internal addition amount is preferably 0.05 parts by weight or more from the viewpoint of rigidity and bulk improving performance, and is preferably 20 parts by weight or less from the viewpoint of the inherent performance of the pulp sheet.

According to the measurement method described later, the improvement rate of the stiffness was determined by using 0.5 to 1.0 parts by weight of the internally added paper quality improver with respect to 100 parts by weight of the pulp, with the pulp sheet not containing the paper quality stiffness improver as a control. Sometimes the stiffness is preferably improved by at least 1%, more preferably by at least 2.5%.

内 The internal addition of the present invention means that it is used as an agent to be added to the pulp slurry during the process of producing the pulp sheet, that is, at the time of papermaking. As the place of addition, before the papermaking process in which the diluted liquid of the pulp raw material is drained while traveling on the wire mesh to form a paper layer, a disintegrator or a beater such as a pulper or a refiner, a machine chest, a head box, or a white water It may be added to a tank such as a tank or a pipe connected to these facilities, but a place where it can be uniformly blended with the pulp raw material, such as a refiner, a machine chest, or a head box, is desirable.

The pulp sheet obtained by using the internally added paper quality improver of the present invention is suitable for newsprint, uncoated printing paper, finely coated printing paper, coated printing paper, information paper, corrugated paper, and white paperboard. Used.

に お い て In the following Production Examples and Examples, “%” and “part” mean “% by weight” and “part by weight” unless otherwise specified.

<Example of emulsion production>
・ Emulsion I
In a 2 L flask equipped with a reflux condenser, a dropping funnel, a thermometer, a nitrogen inlet, and a stirrer, cationic starch A [N% = 0.6%, 7% aqueous solution viscosity 260 mPa · s (50 ° C., B-type viscometer) , Rotor No. 2, 60 rpm)] 48.2 g and ion-exchanged water 695.0 g were charged and heated to 90 ° C to dissolve. After cooling, 29.3 g of Emulgen 150 (nonionic surfactant, 20% aqueous solution, manufactured by Kao Corporation), 1.9 g of 75% phosphoric acid aqueous solution and 17.2 g of 4% sodium hydroxide in 17.2 g of ion-exchanged water in advance. After adding an aqueous solution mixed with 45.0 g, the mixture was stirred at 120 rpm, heated to 60 ° C. while blowing nitrogen, and kept for 30 minutes. Next, 20.4 g of vinyl acetate (manufactured by Shin-Etsu Vinyl Acetate Co., Ltd.) and 1.1 g of initiator (V-50, azo-based initiator, manufactured by Wako Pure Chemical Industries, Ltd.) were dissolved in 29.6 g of ion-exchanged water. Was added and held for 15 minutes. Next, after the temperature was raised to 77 ° C., a mixture of 409.3 g of vinyl acetate, 11.0 g of methacrylic acid (manufactured by Mitsubishi Rayon Co., Ltd.), and 0.9 g of an initiator (V-50) were dissolved in 210 g of ion-exchanged water. These were dropped from respective dropping funnels over 3 hours to carry out polymerization. Next, the temperature was raised to 82 ° C., aged for 1 hour, cooled, and taken out.

(4) A cationic emulsion I having a solid content of 30.8% and an average particle size of 2.63 μm was obtained.

・ Emulsion II
According to the method for producing emulsion I, using the same apparatus, cationic starch A [N% = 0.6%, 7% aqueous solution viscosity 260 mPa · s (50 ° C., B-type viscometer, rotor No. 2, 60 rpm) 48.2 g, polyvinyl alcohol (GL-05, polymerization degree 500, saponification degree 88 mol%, 8.1 g, manufactured by Nippon Synthetic Chemical Co., Ltd.) and ion-exchanged water 585.2 g were charged and heated to 90 ° C. to dissolve. After cooling, 29.3 g of Emulgen 150 (nonionic surfactant, 20% aqueous solution, manufactured by Kao Corporation), 1.9 g of 75% phosphoric acid aqueous solution and 17.2 g of 4% sodium hydroxide in 17.2 g of ion-exchanged water in advance. After adding an aqueous solution mixed with 45.0 g, the mixture was stirred at 120 rpm, heated to 60 ° C. while blowing nitrogen, and kept for 30 minutes. Next, 20.4 g of vinyl acetate (manufactured by Shin-Etsu Vinyl Acetate Co., Ltd.) and 1.1 g of initiator (V-50, azo-based initiator, manufactured by Wako Pure Chemical Industries, Ltd.) were dissolved in 29.6 g of ion-exchanged water. Was added and held for 15 minutes. Next, after the temperature was raised to 77 ° C., a mixture of 205.0 g of vinyl acetate, 5.5 g of methacrylic acid (manufactured by Mitsubishi Rayon Co., Ltd.), 6.6 g of dimethylacrylamide (reagent, manufactured by Wako Pure Chemical Industries, Ltd.), and A solution prepared by dissolving 0.35 g of the initiator (V-50) in 101 g of ion-exchanged water was dropped from each dropping funnel over 3 hours to carry out polymerization. Next, the temperature was raised to 82 ° C., aged for 1 hour, cooled, and taken out.

(4) A cationic emulsion II having a solid content of 23.5% and an average particle diameter of 0.52 μm was obtained.

・ Emulsion III-XIII, XV-XVII
According to Emulsion II, the monomer compositions of the cationic polymer and the polymer particles (B) were changed as shown in Tables 1 and 2, and each was synthesized (note that polyvinyl alcohol was added to 16.1 parts by weight based on 100 parts by weight of the cationic polymer). It was used at a ratio of 8 parts by weight, and the amount of ion-exchanged water was appropriately changed.)

・ Emulsion XIV
The emulsion was synthesized according to the polymerization method of Emulsion II and the monomer composition except that the cationic polymer was excluded. Emulsion XIV having a solid content of 17.7% and an average particle size of 1.85 μm was obtained.

・ Emulsion XVIII
According to the method for producing emulsion I, using the same apparatus, cationic starch A [N% = 0.6%, 7% aqueous solution viscosity 260 mPa · s (50 ° C., B-type viscometer, rotor No. 2, 60 rpm) 28.9 g, polyvinyl alcohol (GL-05, polymerization degree 500, saponification degree 88 mol%, manufactured by Nippon Synthetic Chemical Co., Ltd.) 4.8 g, and ion exchange water 539.7 g were charged and heated to 90 ° C. for dissolution. After cooling, 21.3 g of Emulgen 150 (nonionic surfactant, 20% aqueous solution, manufactured by Kao Corporation), 1.1 g of 75% phosphoric acid aqueous solution and 10.2 g of ion-exchanged water in advance and 4% sodium hydroxide After adding an aqueous solution mixed with 26.6 g, the mixture was stirred at 120 rpm, heated to 60 ° C. while blowing nitrogen, and kept for 30 minutes. Next, 10.7 g of vinyl acetate (manufactured by Shin-Etsu Vinyl Acetate Co., Ltd.) and 1.0 g of initiator (V-50, azo-based initiator, manufactured by Wako Pure Chemical Industries, Ltd.) were dissolved in 9.0 g of ion-exchanged water. Was added and held for 15 minutes. Next, the temperature was raised to 77 ° C., aged for 1 hour, cooled, and taken out.

(4) A cationic emulsion XVIII having a solid content of 7.9% and an average particle size of 0.20 μm was obtained.

・ Emulsion XIX
According to the method for producing emulsion I, using the same apparatus, cationic starch A [N% = 0.6%, 7% aqueous solution viscosity 260 mPa · s (50 ° C., B-type viscometer, rotor No. 2, 60 rpm) 28.9 g, polyvinyl alcohol (GL-05, polymerization degree 500, saponification degree 88 mol%, manufactured by Nippon Synthetic Chemical Co., Ltd.) 4.8 g, and ion exchange water 539.7 g were charged and heated to 90 ° C. for dissolution. After cooling, 21.3 g of Emulgen 150 (nonionic surfactant, 20% aqueous solution, manufactured by Kao Corporation), 1.1 g of 75% phosphoric acid aqueous solution and 10.2 g of ion-exchanged water in advance and 4% sodium hydroxide After adding an aqueous solution mixed with 26.6 g, the mixture was stirred at 120 rpm, heated to 60 ° C. while blowing nitrogen, and kept for 30 minutes. Next, 10.7 g of vinyl acetate (manufactured by Shin-Etsu Vinyl Acetate Co., Ltd.) and 1.0 g of initiator (V-50, azo-based initiator, manufactured by Wako Pure Chemical Industries, Ltd.) were dissolved in 9.0 g of ion-exchanged water. Was added and held for 15 minutes. Next, after the temperature was raised to 77 ° C., a mixture of 54.3 g of vinyl acetate, 1.6 g of methacrylic acid (manufactured by Mitsubishi Rayon Co., Ltd.), 1.9 g of dimethylacrylamide (reagent, manufactured by Wako Pure Chemical Industries, Ltd.), and A solution prepared by dissolving 0.85 g of an initiator (V-50) in 130 g of ion-exchanged water was dropped from each dropping funnel over 3 hours to carry out polymerization. Next, the temperature was raised to 82 ° C., aged for 1 hour, cooled, and taken out.

(4) A cationic emulsion XIX having a solid content of 13.1% and an average particle diameter of 0.43 μm was obtained.

・ Emulsion II-I
Synthesis was carried out according to the polymerization method and the monomer composition of Emulsion XVIII, except that 468.0 g of ion-exchanged water and 175.8 g of Emulgen 150 were used. An emulsion II-I having a solid content of 19.5% and an average particle diameter of 0.22 μm was obtained.

・ Emulsion II-II
Synthesis was carried out in accordance with the polymerization method and the monomer composition of Emulsion XVIII, except that 556.8 g of ion-exchanged water and 35.2 g of polyoxyethylene (50) stearyl ether were used instead of Emulgen 150. Emulsion II-II having a solid content of 20.7% and an average particle diameter of 0.23 μm was obtained.

<Physical property measurement method>
(1) Solid content concentration The solid content concentration in the emulsion was measured by heating 1 g of a sample with an infrared moisture meter (Kett, Infrared Moisture Determination Balance, FD-240) at 150 ° C for 20 minutes.

(2) Method for Measuring Average Particle Size The average particle size of the dispersed particles in the emulsion was measured with a laser diffraction / scattering particle size distribution analyzer LA-910 (manufactured by Horiba, Ltd.). The median diameter was used as the average particle diameter. However, particles having a particle diameter of less than 0.4 μm were measured by a dynamic light scattering particle size distribution analyzer N4Plus (Beckman Coulter, Inc.) in terms of measurement accuracy. In this case, the average particle diameter was determined by a unimodal method (cumulant method).

Examples 1 to 28 and Comparative Examples 1 to 7
Using a paper quality improver (hereinafter also referred to as an agent) comprising the above emulsion, the improvement in rigidity and bulkiness when paper was made from the following pulp raw materials was evaluated. The results are shown in Tables 1 and 2.

[Pulp raw material]
Virgin pulp was used as a pulp raw material in which LBKP (hardwood bleached pulp) was disintegrated and beaten at 25 ° C. with a beater to form a 1% LBKP slurry. This had a Canadian standard freeness (JIS P 8121) of 410 ml.

(Paper making method)
The virgin pulp slurry was weighed out so that the pulp weight of the pulp sheet after papermaking became 70 g / m ² ± 1 g / m ² , and then, as shown in Table 1, the internal paper of Examples or Comparative Examples of the present invention. The quality improver is internally added in an amount of 0.5% to 5% in terms of an effective component (total amount of the natural cationic polymer (A) and the polymer particles (B)) per 100 parts of pulp, and 80 mesh wire is used with a square tappi paper machine. (Area 625 cm ² ) to obtain a pulp sheet. The sheet after papermaking was pressed with a press at 3.5 kg / cm ² for 5 minutes and dried at 105 ° C. for 2 minutes using a mirror-surface dryer. The dried pulp sheet was conditioned at 23 ° C. and a humidity of 50% for one day, and then the tightness of the paper and Clark stiffness were measured by the following methods. Papermaking was performed on 5 sheets each, and the measured value was an average value of 10 times / sheet.

[Evaluation items and methods]
・ Rigidity improvement rate Clark stiffness (according to JIS P8143 method) is determined for each of paper containing a paper quality improver and paper not containing the same, and is calculated by the following equation. The results are shown in Tables 1 and 2. In Example, the rigidity was improved by 7.6% or more at the internal addition amount of 5%, and the rigidity was improved by 2.6% or more at the internal addition amount of 0.5%. In the comparative example, the improvement of the rigidity is 4.8% or less at the internal addition amount of 5%, and the improvement of the rigidity is 1.6% or less at the internal addition amount of 0.5%.
Stiffness improvement rate (%) = (Clark stiffness of paper with added agent / Clark stiffness of paper without added agent-1) × 100

・ Bulk improvement rate:
The tension (according to JIS P8118) is obtained for each of the paper containing the paper quality improver and the paper not containing the paper quality improver, and is calculated by the following equation.
Bulk improvement rate (%) = (1 / tension of paper with added agent-1 / tension of paper with no added agent) / (1 / tension of paper without added agent) × 100

(note)
1) Each cationic polymer is as follows.
-Cationized HEC: manufactured by Wako Pure Chemical Industries, Ltd.-Cationized cellulose: manufactured by Wako Pure Chemical Industries, Ltd.-Ace K-36, K-100, K-250, K-500: Cationized starch (Oji Cornstarch Co., Ltd.) )
・ Cationized starch B: N% = 0.8%, 7% aqueous solution viscosity 2000 mPa · s
-PVA-1: Mercapto-modified polyvinyl alcohol (M-115, polymerization degree 1500, manufactured by Kuraray Co., Ltd.)
-PVA-2: cationized polyvinyl alcohol (C-506, polymerization degree 600, manufactured by Kuraray Co., Ltd.)
2) Each monomer is as follows.
・ VAc: vinyl acetate ・ St: styrene ・ MAA: methacrylic acid ・ AA: acrylamide ・ GMAC: hydroxypropylmethylammonium chloride methacrylate ・ DMAAm: dimethylacrylamide ・ MMA: methyl methacrylate ・ BMA: butyl methacrylate ・ BA: acrylic acid The addition amount of butyl 3) (A) is a percentage by weight based on the vinyl monomer in the monomer composition of the polymer particles (B).

Also, it is expected that the use of emulsions II-I and II-II will provide the same degree of rigidity improvement and bulk improvement as in Examples 1-28.

Claims (9)

An internally added paper quality improver comprising a polymer emulsion containing a natural cationic polymer (A) and polymer particles (B) containing at least a structural unit derived from a vinyl monomer. The internal paper quality improver according to claim 1, wherein the natural cationic polymer (A) is a cationized starch and / or a cationized cellulose. 3. The internally added paper quality improver according to claim 1, wherein the glass transition temperature (Tg) of the polymer particles (B) containing a constitutional unit derived from a vinyl monomer is 90 ° C. or less. The internally added paper quality improver according to any one of claims 1 to 3, wherein the vinyl monomer is a fatty acid vinyl ester. The paper additive of claim 1, wherein the natural cationic polymer (A) has a nitrogen content of 0.05 to 1% by weight. The internal paper quality improver according to any one of claims 1 to 5, wherein the ratio of the natural cationic polymer (A) is 5 to 500 parts by weight based on 100 parts by weight of the polymer particles (B). A pulp sheet in which the internally added paper quality improver according to any one of claims 1 to 6 is present on the surface and / or inside of the pulp sheet. The pulp sheet according to claim 7, wherein the pulp sheet contains 0.05 to 20 parts by weight of the internally added paper quality improver in terms of solid content based on 100 parts by weight of the pulp. A method for improving the paper quality of a pulp sheet, wherein the paper quality improving agent according to any one of claims 1 to 6 is brought into contact with pulp.